In a display device using non-light-emitting optical components, such as a liquid crystal display device, a backlight unit including light sources is disposed behind a display panel, such as a liquid crystal panel, for illuminating the display panel. Brightness of the display panel is adjustable through driving of the light sources with brightness control by an inverter.
Known methods for controlling the brightness of light sources include a voltage dimming control and a plus width modulation (PWM) dimming control. The voltage dimming control is a dimming method in which a voltage applied to the light sources is varied using an inverter. With this method, a wide dimming range cannot be achieved.
The PWM dimming control is a dimming method in which the light sources are periodically turned on and off with modulated turn-on to turn-off period ratios. With this method, a wide dimming range can be achieved by adjusting the turn-on period and the turn-off period. Therefore, the PWM dimming control is widely used in backlight units of liquid crystal display devices.
In a backlight unit using the PWM dimming control for controlling the brightness, roaring sounds may be produced due to second and third harmonics of a dimming frequency during the brightness control of the light source. Such roaring sounds may annoy users and thus should be reduced. To reduce such roaring sounds, a display device including a light-emitting component driving unit in which a dimming frequency for PWM signals is set higher than an upper limit of the audible range of human is disclosed in Patent Document 1.
Patent Document 1: Japanese Published Patent Application No. 2006-114324